COUPLING RATES FROM OSL FOR PATTERN CHANGES TRIGGERED BY CLIMATE CHANGE IN THE TRUNK MISSOURI RIVER BELT DURING THE HOLOCENE: A COUNTER-INTUITIVE UP-DIP MIGRATION IN RESPONSE

NSF/REU and USGS EDMAP students working through University of Texas at Arlington and University of Nebraska at Lincoln mapped the Missouri River Valley floodplain from Yankton, SD to Missouri City, IA (237km) between 2008-2010. Mapping was intended to compare a previously mapped 100km reach 500km downdip in Missouri to determine coupling rates for pattern changes in the river during the Holocene. Particularly, the project aimed to asses if changes from a largely meandering loop system to a heavily braided system observed downdip could be indentified updip, and if so, could comparisons be made between timing and rate of change between updip and downdip parts of the trunk system? Students participating in the field research applied consistent techniques whereby a team of two is assigned a quadrangle and mapping is carried out by hand augering to test consistently between lithofacies association and landforms hypothesized from air photos at multiple sites. Data are collected and interpreted by each team individually and recorded in GIS format. Transitions in loop style indicative of changing river patterns were assessed by dating of discrete loop forms near transitions using optically stimulated luminescence (OSL) testing.

Transition from meandering to braided is rapid updip, occurring at approximately 1.5k.b.p. The transition is more diffuse downdip beginning at 3.5k.b.p. and completing at approximately 1.5k.b.p. The change is basin-wide and presumed to record climate change within the up-dip drainage. Counter to conventional belief, this upstream effect appears to have manifest down-dip first, then complexly migrated up dip.